【effective c++】Design and Declarations I

看一遍忘一遍，觉得还是写点NOTES比较好。就从第四章开始吧。

Item 1: make interfaces easy to use correctly and hard to use incorrectly.

1, creating new types

(*Bad Practise*)
class Date {
public:
  Date(int month, int day, int year);
  ...
};

(*Good practise*)
class Date {
public:
  Date(const Month& month, const Day& day, const Year& year);
  ...
};

2, restrict operations on types, contrain object values

(*Bad Practise*)
struct Month {
  explicit Month(int m):val(m){}
  int m;
};

(*Good practise*)
(*This implementation is better than using enum which is not type safe*)
class Month {
public:
  static Month Jan() {return Month(1);}
  static Month Feb() {return Month(2);}
  ...
private:
  explicit Month(int m):val(m){}
  int m;
};

3, eliminating client resource management responsibility

(*Bad Practise*)
Investment* createInvestment();

(*Good practise*)
(*This implementation is better than using enum which is not type safe*)
std::tr1::shared_ptr createInvestment();
  
};